Method and apparatus with moving object detection

ABSTRACT

A processor-implemented method of detecting a moving object includes: estimating a depth image of a current frame; determining an occlusion image of the current frame by calculating a depth difference value between the estimated depth image of the current frame and an estimated depth image of a previous frame; determining an occlusion accumulation image of the current frame by adding a depth difference value of the occlusion image of the current frame to a depth difference accumulation value of an occlusion accumulation image of the previous frame; and outputting an area of a moving object based on the occlusion accumulation image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 USC § 119(e) of USProvisional Application No. 63/026,228 filed on May 18, 2020, and thebenefit under 35 USC § 119(a) of Korean Patent Application No.10-2020-0113016 filed on Sep. 4, 2020, in the Korean IntellectualProperty Office, the entire disclosures of which are incorporated hereinby reference for all purposes.

BACKGROUND 1. Field

The following description relates to a method and apparatus with movingobject detection.

2. Description of Related Art

A moving object may refer to an object that moves relative to abackground. The moving object may be referred to as a foreground. Anarea that is occluded as the moving object moves may be referred to asan occlusion area. A portion that is newly discovered as the movingobject moves may be referred to as a reappearance area. In general, thebackground may have a greater depth value than the foreground.Therefore, a pixel with a decreasing depth value may be regarded as apixel of the moving object.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In one general aspect, a processor-implemented method of detecting amoving object includes: estimating a depth image of a current frame;determining an occlusion image of the current frame by calculating adepth difference value between the estimated depth image of the currentframe and an estimated depth image of a previous frame; determining anocclusion accumulation image of the current frame by adding a depthdifference value of the occlusion image of the current frame to a depthdifference accumulation value of an occlusion accumulation image of theprevious frame; and outputting an area of a moving object based on theocclusion accumulation image.

The estimating may include: warping coordinates of the depth image ofthe previous frame into coordinates of the depth image of the currentframe based on position information or pose information of a camera; andestimating an area having an inestimable depth value in the depth imageof the current frame using the warped depth image of the previous frame.

The outputting of the area may include outputting the area of the movingobject in a color image, and the area having the inestimable depth valuemay be an area having a depth value that is not estimated by a depthsensor used to generate the depth images due to a position or angledifference between the depth sensor and another sensor used to estimatethe color image.

The determining of the occlusion accumulation image of the current framemay include estimating a depth difference accumulation value of a newlydiscovered area in the occlusion accumulation image of the current framebased on a similarity between a depth value of the depth image of thecurrent frame and the occlusion accumulation image of the previousframe.

The newly discovered area may correspond to an area outside of aboundary of the depth image of the current frame.

The determining of the occlusion accumulation image of the current framemay include initializing a pixel with a depth difference accumulationvalue being less than or equal to a first threshold value in theocclusion accumulation image.

The initializing of the pixel may include initializing the depthdifference accumulation value of the pixel to a value of “0”.

The determining of the occlusion accumulation image of the current framemay include initializing a pixel with a depth difference value beingless than or equal to a second threshold value in the occlusionaccumulation image.

The outputting may include: determining an area including one or morepixels having a depth difference accumulation value being greater than afirst threshold value in the occlusion accumulation image; andoutputting a masking image representing an area of the moving objectbased on the determined area.

A non-transitory computer-readable storage medium may store instructionsthat, when executed by one or more processors, configure the one or moreprocessors to perform the method.

In another general aspect, an apparatus for detecting a moving objectincludes: one or more processors configured to: estimate a depth imageof a current frame, determine an occlusion image of the current frame bycalculating a depth difference value between the estimated depth imageof the current frame and an estimated depth image of a previous frame,determine an occlusion accumulation image of the current frame by addinga depth difference value of the occlusion image of the current frame toa depth difference accumulation value of an occlusion accumulation imageof the previous frame, and output an area of a moving object based onthe occlusion accumulation image.

For the estimating, the one or more processors may be configured to:warp coordinates of the depth image of the previous frame intocoordinates of the depth image of the current frame based on positioninformation or pose information of a camera, and estimate an area havingan inestimable depth value in the depth image of the current frame usingthe warped depth image of the previous frame.

For the determining of the occlusion accumulation image of the currentframe, the one or more processors may be configured to: estimate a depthdifference accumulation value of a newly discovered area in theocclusion accumulation image of the current frame based on a similaritybetween a depth value of the depth image of the current frame and theocclusion accumulation image of the previous frame.

For the determining of the occlusion accumulation image of the currentframe, the one or more processors may be configured to: initialize apixel with a depth difference accumulation value being less than orequal to a first threshold value in the occlusion accumulation image.

For the determining of the occlusion accumulation image of the currentframe, the one or more processors may be configured to: initialize apixel with a depth difference value being less than or equal to a secondthreshold value in the occlusion accumulation image.

For the outputting, the one or more processors may be configured to:obtain an area including one or more pixels having a depth differenceaccumulation value being greater than a first threshold value in theocclusion accumulation image, and output a masking image representing anarea of the moving object based on the obtained area.

The apparatus may include a memory storing instructions that, whenexecuted by the one or more processors, configure the one or moreprocessors to perform the estimating of the depth image of the currentframe, the determining of the occlusion image of the current frame, thedetermining of the occlusion accumulation image of the current frame,and the outputting of the area of the moving object.

In another general aspect, a processor-implemented method of detecting amoving object includes: acquiring a current depth image including anarea in which a depth value is not obtained by a depth sensor;estimating the current depth image, including the area not obtained bythe depth sensor, by warping a previous depth image into coordinates ofthe current depth image; and determining a current occlusion image bycalculating a difference between the estimated depth image and theprevious depth image; determining a current occlusion accumulation imageby adding the current occlusion image to a previous occlusionaccumulation image; and outputting an area of a moving object based onthe current occlusion accumulation image.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of detecting a moving object in an inputimage by a moving object detecting apparatus.

FIG. 2 illustrates an example of a moving object detecting method.

FIG. 3A illustrates an example of a color image that is input.

FIG. 3B illustrates an example of a depth image acquired withoutperforming depth value compensation.

FIG. 3C illustrates an example of an occlusion image acquired withoutperforming depth value compensation.

FIG. 3D illustrates an example of an occlusion accumulation imageacquired without performing depth value compensation.

FIG. 3E illustrates an example of a color image that is input.

FIG. 3F illustrates an example of a depth image acquired by performingdepth value compensation.

FIG. 3G illustrates an example of an occlusion image acquired byperforming depth value compensation.

FIG. 3H illustrates an example of an occlusion accumulation imageacquired by performing depth value compensation.

FIG. 4A illustrates an example of an occlusion image acquired by amoving object detecting apparatus.

FIG. 4B illustrates an example of an occlusion accumulation imageacquired by a moving object detecting apparatus.

FIG. 4C illustrates an example of a masking image acquired by a movingobject detecting apparatus.

FIG. 5A illustrates an example of a color image that is input.

FIG. 5B illustrates an example of a depth image.

FIG. 5C illustrates an example of an occlusion image.

FIG. 5D illustrates an example of an occlusion accumulation image.

FIG. 5E illustrates an example of an occlusion accumulation image.

FIG. 6 illustrates an example of a framework of a moving objectdetecting apparatus.

FIG. 7 illustrates an example of a framework of a moving objectdetecting apparatus.

FIG. 8 illustrates an example of a configuration of a moving objectdetecting apparatus.

Throughout the drawings and the detailed description, unless otherwisedescribed or provided, the same drawing reference numerals will beunderstood to refer to the same elements, features, and structures. Thedrawings may not be to scale, and the relative size, proportions, anddepiction of elements in the drawings may be exaggerated for clarity,illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/orsystems described herein will be apparent after an understanding of thedisclosure of this application. For example, the sequences of operationsdescribed herein are merely examples, and are not limited to those setforth herein, but may be changed as will be apparent after anunderstanding of the disclosure of this application, with the exceptionof operations necessarily occurring in a certain order. Also,descriptions of features that are known in the art, after anunderstanding of the disclosure of this application, may be omitted forincreased clarity and conciseness.

Hereinafter, examples will be described in detail with reference to theaccompanying drawings. However, various alterations and modificationsmay be made to the examples. Here, the examples are not construed aslimited to the disclosure. The examples should be understood to includeall changes, equivalents, and replacements within the idea and thetechnical scope of the disclosure.

The terminology used herein is for the purpose of describing particularexamples only and is not to be limiting of the present disclosure. Asused herein, the singular forms “a”, “an”, and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. As used herein, the term “and/or” includes any one and anycombination of any two or more of the associated listed items. As usedherein, the terms “include,” “comprise,” and “have” specify the presenceof stated features, integers, steps, operations, elements, components,numbers, and/or combinations thereof, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components, numbers, and/or combinations thereof. The use ofthe term “may” herein with respect to an example or embodiment (forexample, as to what an example or embodiment may include or implement)means that at least one example or embodiment exists where such afeature is included or implemented, while all examples are not limitedthereto.

Unless otherwise defined, all terms including technical and scientificterms used herein have the same meaning as commonly understood by one ofordinary skill in the art to which this disclosure pertains consistentwith and after an understanding of the present disclosure. It will befurther understood that terms, such as those defined in commonly-useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thepresent disclosure, and will not be interpreted in an idealized oroverly formal sense unless expressly so defined herein.

When describing the examples with reference to the accompanyingdrawings, like reference numerals refer to like constituent elements anda repeated description related thereto will be omitted. In thedescription of examples, detailed description of well-known relatedstructures or functions will be omitted when it is deemed that suchdescription will cause ambiguous interpretation of the presentdisclosure.

Although terms of “first” or “second” are used herein to describevarious members, components, regions, layers, or sections, thesemembers, components, regions, layers, or sections are not to be limitedby these terms. Rather, these terms are only used to distinguish onemember, component, region, layer, or section from another member,component, region, layer, or section. Thus, a first member, component,region, layer, or section referred to in examples described herein mayalso be referred to as a second member, component, region, layer, orsection without departing from the teachings of the examples.

Throughout the specification, when an element, such as a layer, region,or substrate, is described as being “on,” “connected to,” or “coupledto” another element, it may be directly “on,” “connected to,” or“coupled to” the other element, or there may be one or more otherelements intervening therebetween. In contrast, when an element isdescribed as being “directly on,” “directly connected to,” or “directlycoupled to” another element, there can be no other elements interveningtherebetween. Likewise, expressions, for example, “between” and“immediately between” and “adjacent to” and “immediately adjacent to”may also be construed as described in the foregoing.

The same name may be used to describe an element included in theexamples described above and an element having a common function. Unlessotherwise mentioned, the descriptions on the examples may be applicableto the following examples and thus, duplicated descriptions will beomitted for conciseness.

FIG. 1 illustrates an example of detecting a moving object in an inputimage by a moving object detecting apparatus.

A moving object detecting apparatus may detect a moving object in animage based on depth information. The moving object detecting apparatusmay detect the moving object in the image in a dynamic environment basedon the depth information and on position information and/or poseinformation of a camera. The moving object detecting apparatus maydetect the moving object in the image based on a result of accumulatingdepth value differences. The moving object detecting apparatus maypixelwisely detect the moving object.

The moving object detecting apparatus may recognize an area of themoving object by accumulating depth value differences between a depthimage of a current frame and a depth image of a previous frame. Themoving object detecting apparatus may derive depth value differencesbetween the depth image of the current frame and a depth image of theinitial frame captured by a depth sensor through the process ofaccumulating the depth value differences.

The moving object detecting apparatus may more accurately distinguishbetween the moving object and a background in the dynamic environmentwhere the camera moves. The moving object detecting apparatus of one ormore embodiments may detect the moving object without separate trainingeven when a new environment or object appears in the image. The movingobject detecting apparatus of one or more embodiments may accuratelydetect the moving object even when the moving object occupies many areasof the image. When the object occupies a relatively large portion of theimage compared to the background, the moving object detecting apparatusof one or more embodiments may accurately detect the moving object bystably accumulating depth changes based on the position informationand/or the pose information.

The moving object detecting apparatus of one or more embodiments may notstore the entire background information, and thus the memory usage maynot increase greatly even after time. The moving object detectingapparatus of one or more embodiments may use the image in which depthvalue changes are accumulated and thus, may not need to build a separatebackground map and may have a relatively small operation quantity andmemory usage compared to a typical moving object detecting apparatus.The moving object detecting apparatus of one or more embodiments maypixelwisely detect the area of the moving object and thus, mayaccurately detect the area, compared to detecting the area using abounding box as done by a typical moving object detecting apparatus.Further, even when there is no previous depth information of a newlydiscovered area as the depth sensor moves, the moving object detectingapparatus of one or more embodiments may distinguish the moving objectfrom the background.

Hereinafter, a dynamic environment may refer to an environment where thecamera moves. A static environment refers to an environment where thecamera is fixed. A depth sensor may be a sensor configured to obtaindepth information by capturing an object. The depth sensor may include,for example, a stereo depth sensor, a time of flight (ToF) depth sensor,and/or a structured pattern depth sensor, but are not limited thereto,and may include any or all types of sensors that may obtain depthinformation. A color sensor may be a sensor configured to obtain colorinformation of one or more color channels by capturing an object.

A depth difference value may refer to a difference in depth values, anda depth difference accumulation value may refer to a result ofaccumulating depth difference values. An occlusion image may refer to amap configured with depth difference values. The occlusion image mayinclude both an occlusion area corresponding to a portion that is newlyoccluded as a moving object moves and a reappearance area correspondingto a portion that newly appears as the moving object moves. An occlusionaccumulation image may refer to a map configured with depth differenceaccumulation values. Position information of a camera may refer tothree-dimensional (3D) coordinates of a position of the camera, and poseinformation of the camera may refer to a direction that the camera facesat a fixed position. The position information and the pose informationof the camera may represent a 6-degree of freedom (DoF) physicalquantity.

The moving object detecting apparatus may use visual odometry toestimate the 6-DoF position information and pose information of thecamera based on image information of the camera, but is not limitedthereto. The position information and pose information of the camera maybe obtained in various manners. Visual odometry may be referred to asimage navigation. Image navigation may include a feature-based methodand a density-based method, but is not limited thereto, and may includeall kinds of algorithms for estimating the position of an object throughan image.

To this end, the moving object detecting apparatus may perform occlusionaccumulation, depth compensation, and occlusion prediction on a newlydiscovered area. In the occlusion accumulation, the moving objectdetecting apparatus may recognize a moving object by accumulating depthvalue differences of a depth sensor. The moving object detectingapparatus may obtain differences between consecutive depth values ofcorresponding pixels, and acquire an occlusion accumulation image byaccumulating the differences.

The moving object detecting apparatus may warp a depth image of aprevious frame into a depth image of a current frame based on theposition information and pose information of the camera. Through this,the moving object detecting apparatus may acquire a depth imageconsidering a movement of the camera. Here, image warping may be a typeof geometric transformation, and may refer to an operation oftransforming a pixel at (x, y) coordinates in a previous frame to apixel at (x′, y′) coordinates in a current frame.

The moving object detecting apparatus may acquire an occlusion image bycalculating a depth value difference of a depth image in which themovement of the camera is compensated. When there appears no change in adepth image in which a pose is corrected in an environment without amoving object, the occlusion image may not have any value. When there isa moving object, the background may be occluded by the moving object,and thus the depth may change, such that the shape of the moving objectmay appear in the occlusion image. When occlusion images arecontinuously accumulated, the accumulation value may change along atrajectory of the moving object. When the acquired occlusionaccumulation image is initialized based on a threshold value, the movingobject may be clearly and accurately distinguished. Initializing theocclusion accumulation image based on the threshold value may bereferred to as truncation in the sense of initializing a value less thanthe threshold value to a predetermined value.ΔZ _(i)(u, ξ_(i) ^(i+1))=Z _(i)(w(u, ξ_(i) ^(i+1)))−Z _(i+1) (u)  Equation 1:

Equation 1 above is a formula for calculating a depth difference valueto acquire an occlusion image, for example. Z denotes a depth value.ΔZ_(i) greater than 0 indicates the depth value decreases, which mayindicate the background is occluded by a moving object and thus,represents an occlusion area. ΔZ_(i) less than or equal to 0 indicatesthe depth value increases, which may indicate that the backgroundreappears from the moving object and thus, represents a reappearancearea.

ξ_(i) ^(i+1) denotes a parameter of the camera between an i^(th) frameand an (i+1)^(th) frame. For example, the parameter of the camera mayinclude position information and pose information and may be 6-DoFinformation. W denotes a warping function. W(u, ξ_(i) ^(i+1)) denotes apixel of the i^(th) frame corresponding to a pixel u of the (i+1)^(th)frame based on the parameter of the camera. Consequently, Equation 1expresses a depth value difference between the (i+1)^(th) frame and thei^(th) frame with respect to the pixel u.W(u, ξ_(i) ^(i+1))=π(exp(ξ_(i) ^(i+1))π⁻¹ (u, Z _(i)(u))   Equation 2:

Equation 2 above is a formula that describes the warping function inmore detail, for example. π denotes a project function that maps a 3Dpoint to a pixel of a 2D image. exp(ξ_(i) ^(i+1)) denotes atransformation matrix for the camera parameter ξ_(i) ^(i+1).A _(i+1)(u)=ΔZ _(i)(u, ξ_(i) ^(i+1))+{tilde over (A)}_(i) (W(u, ξ_(i)^(i+1)))   Equation 3:

Equation 3 above is a formula for obtaining a depth differenceaccumulation value to acquire an occlusion accumulation image, forexample. A_(i+1) (u) denotes a depth difference accumulation value forthe pixel u of the (i+1)^(th) frame. denotes a depth differenceaccumulation value that is processed based on the threshold value, thatis, processed through truncation. According to Equation 3, the depthdifference accumulation value of the (i+1)^(th) frame is a result ofadding the depth difference value between the i^(th) frame and the(i+1)^(th) frame to the depth difference accumulation value of thei^(th) frame.

Equation 4:

$\begin{matrix}{\approx {{\Delta\;{Z_{i}\left( {u,\xi_{i}^{i + 1}} \right)}} + {\sum\limits_{k = 1}^{i}{\Delta\;{Z_{k}\left( {{w\left( {u,\xi_{k + 1}^{i}} \right)},\xi_{k}^{k + 1}} \right)}}}}} \\{\approx {{Z_{k_{u}}\left( {w\left( {u,\xi_{k_{u}}^{i + 1}} \right)} \right)} - {Z_{i + 1}(u)}}}\end{matrix}$

When the truncation is not triggered, A(u)=Ã(u) is satisfied, and thus

Equation 3 may be approximated to Equation 4 above, for example. Here,k_(u) denotes an index of a frame where the pixel u of the current frameis first observed. In the end, when the truncation is not triggered, theocclusion accumulation image of the (i+1)^(th) frame may be approximatedto a difference between the depth value of the pixel u of the (i+1)^(th)frame and a depth value of a pixel corresponding to the pixel u in theframe in which the pixel u first appears.

The result of approximation in Equation 4 indicates the differencebetween the depth value of the current frame and the depth value of theframe in which the corresponding area first appears, which, however, isestablished because the truncation is not triggered. When the depthvalue of a current frame is simply subtracted from the depth value of afirst frame, a reappearance area may not be processed due to themovement of the camera and the movement of the moving object, such thatthe background and the moving object may not be clearly and/oraccurately distinguished.{tilde over (A)}_(i)(u)=0 for A _(i)(u)≤τ_(α)(u)   Equation 5:{tilde over (A)}_(i)(u)=0 for ΔZ_(i)(u, ξ_(i) ^(i+1))≤−τ_(β)(u)  Equation 6:

Equations 5 and 6 above are formulas for processing the reappearancearea through the truncation of the occlusion accumulation image, forexample. According to Equation 5, when the depth difference accumulationvalue A_(i)(u ) in the occlusion accumulation image is less than a firstthreshold value τ_(α)(u), the depth difference accumulation value may beinitialized to “0”. Equation 5 indicates initializing the reappearingbackground area by initializing the depth difference accumulation valueto “0” when the depth difference accumulation value is close to “0” ornegative.

According to Equation 6, when the depth difference value ΔZ_(i) (u,ξ_(i) ^(i+1)) in the occlusion accumulation image is less than a secondthreshold value , the depth difference accumulation value may beinitialized to “0”. In the occlusion accumulation image, there may occuran error of the depth value increasing as the distance between the depthsensor and the captured object increases and an error in the pose valueof the camera. When the background reappears, and the depth differencevalue is not exactly “0” but is greater than “0”, the background may bemisrecognized as the moving object.

For example, as the moving object passes, the depth value may changefrom 5 m to 1 m and then to 3 m. Here, the depth value of 3 m is a casewhere the depth value is failed to return to 5 m due to an error. Due tothe depth difference value 2 m between 3 m and 1 m, the correspondingarea may be recognized as an area of the moving object. In this case,Equation 6 indicates initializing the corresponding area to thebackground. The moving object detecting apparatus may initialize thearea to the background if the depth difference value is less than thesecond threshold value according to Equation 6.

Referring to FIG. 1, an occlusion image 110 represents a moving objectusing a white boundary and a black boundary. The moving object is movingleftward, and thus a left boundary 111 of the moving object is marked inwhite. A right boundary 113 of the moving object is marked in black. Inan example, the left boundary 111 may correspond to an occlusion areaand the right boundary 113 may correspond to a reappearance area. Anocclusion accumulation image 130 may be acquired by accumulating theocclusion image 110. As a reappearance area is initialized, theocclusion accumulation image 130 shows a result 131 of accumulating anocclusion area. The result 131 of accumulating the occlusion area maycorrespond to the area of the moving object of a current frame.

The moving object detecting apparatus may output a masking image 153that distinguishes the area of the moving object from the background.The masking image 153 may be an image representing the boundary of themoving object by moving object segmentation. A portion representing themoving object may be referred to as a masking area. For example, themasking area may be filled with a single color. The background area andthe masking area may be distinguished by “0” and “1”. In a color image150, the masking image 153 shows a result of accurately matching to amoving object 151.

In the depth compensation, the moving object detecting apparatus maycompensate for the depth value based on position information or poseinformation of the depth sensor. When the depth value is notcompensated, an error may occur during the occlusion accumulation. Themoving object detecting apparatus of one or more embodiments maycompensate for unmeasured depth values around the moving object bywarping the depth value of a previous frame before accumulating thedepth value differences.

A general depth sensor may not estimate or measure a depth value nearthe boundary of an object due to an error of the general depth sensor.In such an area where the depth value cannot be estimated, anunnecessary stripe pattern may be generated, and a clean (or clear oraccurate) occlusion accumulation image may not be derived. To solve thisproblem, the moving object detecting apparatus of one or moreembodiments may compensate for a portion with an unestimated orunmeasured depth value.

In the occlusion accumulation prediction, the moving object detectingapparatus may predict a depth difference accumulation value of an areanewly discovered by the depth sensor based on a similarity between thedepth value and the occlusion accumulation image. When an area that hasnot been captured before is newly captured, there may be no depth valueto be compared. In this case, the depth difference accumulation value ofthe area that has not been compared may not be calculated and thus, maybe set to, for example, a default value. The moving object detectingapparatus may average pixel values of adjacent occlusion accumulationimages and estimate the depth difference accumulation value based on theresult.

Since this estimation process may be performed when there is a depthdifference accumulation value for a nearby pixel, the moving objectdetecting apparatus may repeatedly perform the estimation process untilall pixels for the newly discovered area are processed. Through theestimation process, a pixel, the depth value of which is highly likelyto change, may have a value estimated by the estimation process. Whenthe moving object is distinguished by truncating the accumulation imagebased on a predetermined criterion, the moving object may be accuratelydistinguished even for an area that has not been captured before and hasno depth value to be compared.

FIG. 2 illustrates an example of a moving object detecting method.

In operation 201, a moving object detecting apparatus may estimate adepth image of a current frame. An index of the current frame may be i+1of Equation 1. The moving object detecting apparatus may preprocess thedepth image. The moving object detecting apparatus may warp coordinatesof a depth image of a previous frame into coordinates of the depth imageof the current frame based on position information or pose informationof a camera. The moving object detecting apparatus may estimate an areahaving an inestimable depth value that is not estimated (or cannot beaccurately estimated) by the depth sensor in the depth image of thecurrent frame using the warped depth image of the previous frame.

In operation 203, the moving object detecting apparatus may acquire anocclusion image of the current frame by calculating a depth differencevalue between the estimated depth image of the current frame and anestimated depth image of the previous frame. For example, a pixel of theocclusion image of the current frame may be acquired by calculating adepth difference value between a corresponding pixel of the estimateddepth image of the current frame and a corresponding pixel of theestimated depth image of the previous frame. An index of the previousframe is i of Equation 1. The depth difference value may be ΔZ_(i) ofEquation 1 above, for example.

In operation 205, the moving object detecting apparatus may acquire anocclusion accumulation image of the current frame by adding a depthdifference value of the occlusion image of the current frame to a depthdifference accumulation value of an occlusion accumulation image of theprevious frame. For example, a depth difference accumulation value of apixel of the occlusion accumulation image of the current frame may beacquired by adding a depth difference value of a corresponding pixel ofthe occlusion image of the current frame to a depth differenceaccumulation value of a corresponding pixel of an occlusion accumulationimage of the previous frame.

The moving object detecting apparatus may acquire the occlusionaccumulation image that is more accurately mapped to the moving objectby performing truncation on a reappearance area. For example, the movingobject detecting apparatus may initialize a pixel with a depthdifference accumulation value being less than or equal to a firstthreshold value in the occlusion accumulation image. For example, whenthe depth difference accumulation value of the pixel is close to “0” ornegative, the moving object detecting apparatus may initialize areappearing background area by initializing the depth differenceaccumulation value to “0”.

To remove errors occurring in the occlusion accumulation image due to anerror of the depth value increasing as the distance between the depthsensor and the captured object increases and an error in the pose valueof the camera, the moving object detecting apparatus may initialize thereappearance area. The moving object detecting apparatus may initializea pixel with a depth difference value being less than or equal to asecond threshold value in the occlusion accumulation image. When thedepth difference value is less than the second threshold value, themoving object detecting apparatus may initialize the corresponding areato the background.

In operation 207, the moving object detecting apparatus may output anarea of the moving object based on the occlusion accumulation image. Themoving object detecting apparatus may obtain an area including one ormore pixels having a depth difference accumulation value being greaterthan a first threshold value in the occlusion accumulation image. Themoving object detecting apparatus may output a masking imagerepresenting the area of the moving object based on the obtained area.The masking area may be filled with a single color. The background areaand the masking area may be distinguished by “0” and “1”, respectively.

Hereinafter, FIGS. 3A to 3D are provided to describe noise appearing inan occlusion accumulation image acquired without performing depth valuecompensation. FIG. 3A illustrates an example of a color image that isinput. FIG. 3B illustrates an example of a depth image acquired withoutperforming depth value compensation. FIG. 3C illustrates an example ofan occlusion image acquired without performing depth value compensation.FIG. 3D illustrates an example of an occlusion accumulation imageacquired without performing depth value compensation.

FIG. 3A shows a color image that is input, where the color imageincludes a moving object 300 and a background 309. FIG. 3B shows a depthimage acquired without performing depth value compensation, where amoving object 302 is displayed in the depth image. Due to physicallimitations such as a position or angle difference between a depthsensor and a color sensor, there may be an area having an inestimabledepth value in the vicinity of a boundary of an object. An area havingan inestimable depth value may be an area in which a depth value is notestimated, or is not accurately estimated, by the depth sensor due tothe physical limitations such as the position or the angle differencebetween the depth sensor and the color sensor. Black areas 301 and 303shown on the left and right sides of the moving object 302 areinestimable areas. The slanted black areas on the edges of the depthimage are portions generated when the depth image is warped into thecoordinates of the color image.

When the depth image of FIG. 3B is a depth image of a current frame, theocclusion image of FIG. 3C may be acquired by obtaining the depth imageof FIG. 3B and a depth value difference between a depth image of aprevious frame and the depth image of FIG. 3B. The moving object ismoving rightward. An occlusion area 305 appears on the right side of themoving object, and a reappearance area 304 appears on the left side ofthe moving object.

FIG. 3D shows the occlusion accumulation image acquired by accumulatingthe occlusion image of FIG. 3C. When a general depth sensor is used, anarea having an inestimable depth value may be generated in the vicinityof the boundary of the object due to measurement errors. An undesiredstripe pattern 307 may be generated by the area having an inestimabledepth value, such that a clear and/or accurate occlusion accumulationimage cannot be acquired. A white area 306 corresponds to a depth valuedifference between the current frame and a frame (k_(u) of Equation 4,for example) in which the area first appears, for an area where themoving object of the current frame is present. A dark gray area 308corresponds to a depth value difference between the current frame andthe frame (k_(u) of Equation 4, for example) in which the area firstappears, for an area where the moving object of the first frame ispresent.

Hereinafter, FIGS. 3E to 3H are provided to describe noise appearing inan occlusion accumulation image acquired by performing depth valuecompensation. FIG. 3E illustrates an example of a color image that isinput. FIG. 3F illustrates an example of a depth image acquired byperforming depth value compensation. FIG. 3G illustrates an example ofan occlusion image acquired by performing depth value compensation. FIG.3H illustrates an example of an occlusion accumulation image acquired byperforming depth value compensation.

FIG. 3E shows a color image that is input, where the color imageincludes a moving object 310 and a background 319. The moving objectdetecting apparatus may warp a depth image of a previous frame intocoordinates of a current frame in view of a change in the pose of thecamera. The moving object detecting apparatus may compensate for a depthvalue of an area of which the depth value in the previous frame isobtained but the depth value in the current frame is not. FIG. 3F showsa depth image acquired by performing depth value compensation, where amoving object 312 is displayed in the depth image. Compared to the depthimage of FIG. 3B, an inestimable area is removed through the depth valuecompensation. The slanted black areas on the edges of the depth imageare portions generated when the depth image is warped into thecoordinates of the color image.

When the depth image of FIG. 3F is a depth image of a current frame, theocclusion image of FIG. 3G may be acquired by obtaining the depth imageof FIG. 3F and a depth value difference between a depth image of aprevious frame and the depth image of FIG. 3F. The moving object ismoving rightward. An occlusion area 315 appears on the right side of themoving object, and a reappearance area 314 appears on the left side ofthe moving object.

FIG. 3H shows the occlusion accumulation image acquired by accumulatingthe occlusion image of FIG. 3G. The moving object detecting apparatusmay acquire a clean (e.g., clear or accurate) occlusion accumulationimage by accumulating compensated depth images. Compared to FIG. 3D, aclean (e.g., clear or accurate) occlusion accumulation image notincluding the stripe pattern 307 is acquired. A white area 316corresponds to a depth value difference between the current frame and aframe (k_(u) of Equation 4, for example) in which the area firstappears, for an area where the moving object of the current frame ispresent. A dark gray area 318 corresponds to a depth value differencebetween the current frame and the frame (k_(u) of Equation 4, forexample) in which the area first appears, for an area where the movingobject of the first frame is present. Thereafter, the moving objectdetecting apparatus may distinguish the moving object by truncating theocclusion accumulation image based on a predetermined criterion.

FIG. 4A illustrates an example of an occlusion image acquired by amoving object detecting apparatus. FIG. 4B illustrates an example of anocclusion accumulation image acquired by the moving object detectingapparatus. FIG. 4C illustrates an example of a masking image acquired bythe moving object detecting apparatus.

Referring to FIG. 4A, a moving object detecting apparatus may acquire anocclusion image by calculating a depth value difference between a depthimage of a current frame and a depth image of a previous frame. In FIG.4A, a moving object (a person, for example) has both arms down (whereboth arms are moving down, for example). Accordingly, occlusion areas402 appear at the lower boundaries of the arms, and reappearance areas401 appear at the upper boundaries of the arms.

Referring to FIG. 4B, an occlusion accumulation image acquired byaccumulating the occlusion image of FIG. 4A over time is shown. In FIG.4B, an area 403 of the moving object of the current frame is clearlydisplayed.

Referring to FIG. 4C, the moving object detecting apparatus may generatea masking image 405 by separating the area of the moving object and thebackground in the image of FIG. 4B. When the masking image 405 is mappedto a color image, the moving object 404 and the masking image 405 may bemapped with high accuracy.

Hereinafter, FIGS. 5A to 5E are provided to describe an occlusionaccumulation image that changes depending on whether or not a new areais estimated. FIG. 5A illustrates an example of a color image that isinput. FIG. 5B illustrates an example of a depth image. FIG. 5Cillustrates an example of an occlusion image. FIG. 5D illustrates anexample of an occlusion accumulation image without a new area estimated.FIG. 5E illustrates an example of an occlusion accumulation image with anew area estimated.

A moving object detecting apparatus may estimate a depth differenceaccumulation value of a newly discovered area in an occlusionaccumulation image of a current frame based on a similarity between adepth value of a depth image of the current frame and an occlusionaccumulation image of a previous frame.

FIG. 5A shows a color image that is input, where a moving object 501 ismoving. FIG. 5B shows a depth image, where since the moving object has asmaller depth value than the background, an area 502 of the movingobject is represented in a darker gray compared to the background. Theblack boundaries on the edges of the screen are generated when the depthimage is converted into the coordinates of the color image. FIG. 5Cshows an occlusion image, where the boundary of an area 503 of themoving object is represented in white or black due to the movement ofthe moving object. A black boundary 504 appears due to the boundary ofthe camera screen.

FIG. 5D illustrates an example of an occlusion accumulation imagewithout a new area estimated. When a moving camera discovers a new areaoutside the black boundary 504 of FIG. 5C, there is no depth value tocompare because the previous frame does not include the new area. Thus,a new area 505 having the same depth difference accumulation value asthe background appears in the occlusion accumulation image, and an area506 displayed in the occlusion accumulation image fails to clearlyrepresent the area of the moving object.

FIG. 5E illustrates an example of an occlusion accumulation image with anew area estimated. The moving object detecting apparatus may estimate adepth difference accumulation value of the new area based on asimilarity between the depth value of the current frame and theocclusion accumulation image of the previous frame. Since thisestimation process may be performed when there is a depth differenceaccumulation value for a nearby pixel, the moving object detectingapparatus may repeatedly perform the estimation process until all pixelsfor the newly discovered area are processed. Consequently, an area 507displayed in the occlusion accumulation image clearly and accuratelyrepresents the area of the moving object.

FIG. 6 illustrates an example of a framework of a moving objectdetecting apparatus.

Referring to FIG. 6, pose information 601 of a depth sensor and a depthimage 602 may be provided as inputs. In addition to the pose information601 of the depth sensor, position information of the depth sensor may befurther provided. In an example, the pose information 601 furtherincludes the position information of the depth sensor.

In operation 603, a moving object detector 605 may receive the poseinformation 601 of the depth sensor. The moving object detector 605 mayfurther receive the position information of the depth sensor. The poseinformation 601 and/or the position information of the depth sensor maybe received from an external device or may be received from anotherelement in the moving object detecting apparatus. In operation 604, themoving object detector 605 may receive the depth image 602.

The moving object detector 605 may estimate a depth value of aninestimable area using the pose information 601 or position informationof the depth sensor. The moving object detector 605 may acquire anocclusion image from a depth value difference between a current frameand a previous frame. The moving object detector 605 may acquire anocclusion accumulation image by accumulating the occlusion image.

The moving object detector 605 may estimate a depth differenceaccumulation value with respect to a newly discovered area. Ifperformed, a portion where a depth difference occurs may be recognizedas the moving object. The moving object detector 605 may estimate thedepth difference accumulation value of the new area based on asimilarity between the depth value of the current frame and theocclusion accumulation image of the current frame. Consequently, themoving object detector 605 may acquire an area 606 of the moving objectwith high accuracy.

FIG. 7 illustrates an example of a framework of a moving objectdetecting apparatus.

Referring to FIG. 7, pose information 706 of a depth sensor may beobtained by visual odometry 705. In operation 703, a color image 701 maybe input into a moving object detector 707 and the visual odometry 705.In operation 704, a depth image 702 may be input into the moving objectdetector 707 and the visual odometry 705. In operation 709, an area 708of the moving object of the previous frame may be input into the visualodometry 705. The visual odometry 705 may receive the color image 701,the depth image 702, and the area 708 of the moving object of theprevious frame and output the pose information 706 of the depth sensor.

The moving object detector 707 may estimate a depth value of aninestimable area using the pose information 706 or position informationof the depth sensor. The moving object detector 707 may acquire anocclusion image from a depth value difference between a current frameand a previous frame. The moving object detector 707 may acquire anocclusion accumulation image by accumulating the occlusion image.

The moving object detector 707 may estimate a depth differenceaccumulation value with respect to a newly discovered area. Ifperformed, a portion where a depth difference occurs may be recognizedas the moving object. The moving object detector 707 may estimate thedepth difference accumulation value of the new area based on asimilarity between the depth value of the current frame and theocclusion accumulation image of the current frame. In operation 718, themoving object detector 707 may output an area 708 of the moving objectto be transferred to the visual odometry 705.

FIG. 8 illustrates an example of a configuration of a moving objectdetecting apparatus.

Referring to FIG. 8, a moving object detecting apparatus 800 includes atleast one processor 801 (e.g., one or more processors) and a memory 803.The moving object detecting apparatus 800 may further include a depthsensor 805 and/or a color sensor 807.

The processor 801 may estimate a depth image of a current frame. Theprocessor 801 may acquire an occlusion image of the current frame bycalculating a depth difference value between the estimated depth imageof the current frame and an estimated depth image of a previous frame.The processor 801 may acquire an occlusion accumulation image of thecurrent frame by adding a depth difference value of the occlusion imageof the current frame to a depth difference accumulation value of anocclusion accumulation image of the previous frame. The processor 801may output an area of the moving object based on the occlusionaccumulation image.

The processor 801 may warp coordinates of a depth image of a previousframe into coordinates of the depth image of the current frame based onposition information or pose information of a camera. The processor 801may estimate an area having an inestimable depth value in the depthimage of the current frame using the warped depth image of the previousframe.

The processor 801 may estimate a depth difference accumulation value ofa newly discovered area in an occlusion accumulation image of a currentframe based on a similarity between a depth value of a depth image ofthe current frame and an occlusion accumulation image of a previousframe.

The processor 801 may initialize a pixel with a depth differenceaccumulation value being less than or equal to a first threshold valuein the occlusion accumulation image. The processor 801 may initialize apixel with a depth difference value being less than or equal to a secondthreshold value in the occlusion accumulation image.

The processor 801 may obtain an area including one or more pixels havinga depth difference accumulation value being greater than a firstthreshold value in the occlusion accumulation image. The processor 801may output a masking image representing the area of the moving objectbased on the obtained area.

The moving object detectors, moving object detectors, moving objectdetecting apparatuses, processors, memories, depth sensors, colorsensors, moving object detector 605, moving object detector 707, movingobject detecting apparatus 800, processor 801, memory 803, depth sensor805, color sensor 807, and other apparatuses, devices, units, modules,and components described herein with respect to FIGS. 1-8 areimplemented by or representative of hardware components. Examples ofhardware components that may be used to perform the operations describedin this application where appropriate include controllers, sensors,generators, drivers, memories, comparators, arithmetic logic units,adders, subtractors, multipliers, dividers, integrators, and any otherelectronic components configured to perform the operations described inthis application. In other examples, one or more of the hardwarecomponents that perform the operations described in this application areimplemented by computing hardware, for example, by one or moreprocessors or computers. A processor or computer may be implemented byone or more processing elements, such as an array of logic gates, acontroller and an arithmetic logic unit, a digital signal processor, amicrocomputer, a programmable logic controller, a field-programmablegate array, a programmable logic array, a microprocessor, or any otherdevice or combination of devices that is configured to respond to andexecute instructions in a defined manner to achieve a desired result. Inone example, a processor or computer includes, or is connected to, oneor more memories storing instructions or software that are executed bythe processor or computer. Hardware components implemented by aprocessor or computer may execute instructions or software, such as anoperating system (OS) and one or more software applications that run onthe OS, to perform the operations described in this application. Thehardware components may also access, manipulate, process, create, andstore data in response to execution of the instructions or software. Forsimplicity, the singular term “processor” or “computer” may be used inthe description of the examples described in this application, but inother examples multiple processors or computers may be used, or aprocessor or computer may include multiple processing elements, ormultiple types of processing elements, or both. For example, a singlehardware component or two or more hardware components may be implementedby a single processor, or two or more processors, or a processor and acontroller. One or more hardware components may be implemented by one ormore processors, or a processor and a controller, and one or more otherhardware components may be implemented by one or more other processors,or another processor and another controller. One or more processors, ora processor and a controller, may implement a single hardware component,or two or more hardware components. A hardware component may have anyone or more of different processing configurations, examples of whichinclude a single processor, independent processors, parallel processors,single-instruction single-data (SISD) multiprocessing,single-instruction multiple-data (SIMD) multiprocessing,multiple-instruction single-data (MISD) multiprocessing, andmultiple-instruction multiple-data (MIMD) multiprocessing.

The methods illustrated in FIGS. 1-8 that perform the operationsdescribed in this application are performed by computing hardware, forexample, by one or more processors or computers, implemented asdescribed above executing instructions or software to perform theoperations described in this application that are performed by themethods. For example, a single operation or two or more operations maybe performed by a single processor, or two or more processors, or aprocessor and a controller. One or more operations may be performed byone or more processors, or a processor and a controller, and one or moreother operations may be performed by one or more other processors, oranother processor and another controller. One or more processors, or aprocessor and a controller, may perform a single operation, or two ormore operations.

Instructions or software to control computing hardware, for example, oneor more processors or computers, to implement the hardware componentsand perform the methods as described above may be written as computerprograms, code segments, instructions or any combination thereof, forindividually or collectively instructing or configuring the one or moreprocessors or computers to operate as a machine or special-purposecomputer to perform the operations that are performed by the hardwarecomponents and the methods as described above. In one example, theinstructions or software include machine code that is directly executedby the one or more processors or computers, such as machine codeproduced by a compiler. In another example, the instructions or softwareincludes higher-level code that is executed by the one or moreprocessors or computer using an interpreter. The instructions orsoftware may be written using any programming language based on theblock diagrams and the flow charts illustrated in the drawings and thecorresponding descriptions used herein, which disclose algorithms forperforming the operations that are performed by the hardware componentsand the methods as described above.

The instructions or software to control computing hardware, for example,one or more processors or computers, to implement the hardwarecomponents and perform the methods as described above, and anyassociated data, data files, and data structures, may be recorded,stored, or fixed in or on one or more non-transitory computer-readablestorage media. Examples of a non-transitory computer-readable storagemedium include read-only memory (ROM), random-access programmable readonly memory (PROM), electrically erasable programmable read-only memory(EEPROM), random-access memory (RAM), dynamic random access memory(DRAM), static random access memory (SRAM), flash memory, non-volatilememory, CD-ROMs, CD−Rs, CD+Rs, CD−RWs, CD+RWs, DVD-ROMs, DVD−Rs, DVD+Rs,DVD−RWs, DVD+RWs, DVD-RAMs, BD-ROMs, BD-Rs, BD-R LTHs, BD-REs, blue-rayor optical disk storage, hard disk drive (HDD), solid state drive (SSD),flash memory, a card type memory such as multimedia card micro or a card(for example, secure digital (SD) or extreme digital (XD)), magnetictapes, floppy disks, magneto-optical data storage devices, optical datastorage devices, hard disks, solid-state disks, and any other devicethat is configured to store the instructions or software and anyassociated data, data files, and data structures in a non-transitorymanner and provide the instructions or software and any associated data,data files, and data structures to one or more processors or computersso that the one or more processors or computers can execute theinstructions. In one example, the instructions or software and anyassociated data, data files, and data structures are distributed overnetwork-coupled computer systems so that the instructions and softwareand any associated data, data files, and data structures are stored,accessed, and executed in a distributed fashion by the one or moreprocessors or computers.

While this disclosure includes specific examples, it will be apparentafter an understanding of the disclosure of this application thatvarious changes in form and details may be made in these exampleswithout departing from the spirit and scope of the claims and theirequivalents. The examples described herein are to be considered in adescriptive sense only, and not for purposes of limitation. Descriptionsof features or aspects in each example are to be considered as beingapplicable to similar features or aspects in other examples. Suitableresults may be achieved if the described techniques are performed in adifferent order, and/or if components in a described system,architecture, device, or circuit are combined in a different manner,and/or replaced or supplemented by other components or theirequivalents.

What is claimed is:
 1. A processor-implemented method of detecting amoving object, the method comprising: estimating a depth image of acurrent frame; determining an occlusion image of the current frame bycalculating a depth difference value between the estimated depth imageof the current frame and an estimated depth image of a previous frame;determining an occlusion accumulation image of the current frame byadding a depth difference value of the occlusion image of the currentframe to a depth difference accumulation value of an occlusionaccumulation image of the previous frame; and outputting an area of amoving object based on the occlusion accumulation image, wherein thedetermining of the occlusion accumulation image of the current framecomprises estimating a depth difference accumulation value of a newlydiscovered area in the occlusion accumulation image of the current framebased on a similarity between a depth value of the depth image of thecurrent frame and the occlusion accumulation image of the previousframe.
 2. The method of claim 1, wherein the estimating comprises:warping coordinates of the depth image of the previous frame intocoordinates of the depth image of the current frame based on positioninformation or pose information of a camera; and estimating an areahaving an inestimable depth value in the depth image of the currentframe using the warped depth image of the previous frame.
 3. The methodof claim 2, wherein the outputting of the area comprises outputting thearea of the moving object in a color image, and the area having theinestimable depth value is an area having a depth value that is notestimated by a depth sensor used to generate the depth images due to aposition or angle difference between the depth sensor and another sensorused to estimate the color image.
 4. The method of claim 1, wherein thenewly discovered area corresponds to an area outside of a boundary ofthe depth image of the current frame.
 5. The method of claim 1, whereinthe determining of the occlusion accumulation image of the current framecomprises initializing a pixel with a depth difference accumulationvalue being less than or equal to a first threshold value in theocclusion accumulation image.
 6. The method of claim 5, wherein theinitializing of the pixel comprises initializing the depth differenceaccumulation value of the pixel to a value of “0”.
 7. The method ofclaim 1, wherein the determining of the occlusion accumulation image ofthe current frame comprises initializing a pixel with a depth differencevalue being less than or equal to a second threshold value in theocclusion accumulation image.
 8. The method of claim 1, wherein theoutputting comprises: determining an area including one or more pixelshaving a depth difference accumulation value being greater than a firstthreshold value in the occlusion accumulation image; and outputting amasking image representing an area of the moving object based on thedetermined area.
 9. A non-transitory computer-readable storage mediumstoring instructions that, when executed by one or more processors,configure the one or more processors to perform the method of claim 1.10. An apparatus for detecting a moving object, the apparatuscomprising: one or more processors configured to: estimate a depth imageof a current frame, determine an occlusion image of the current frame bycalculating a depth difference value between the estimated depth imageof the current frame and an estimated depth image of a previous frame,determine an occlusion accumulation image of the current frame by addinga depth difference value of the occlusion image of the current frame toa depth difference accumulation value of an occlusion accumulation imageof the previous frame, and output an area of a moving object based onthe occlusion accumulation image, wherein, for the determining of theocclusion accumulation image of the current frame, the one or moreprocessors are configured to estimate a depth difference accumulationvalue of a newly discovered area in the occlusion accumulation image ofthe current frame based on a similarity between a depth value of thedepth image of the current frame and the occlusion accumulation image ofthe previous frame.
 11. The apparatus of claim 10, wherein, for theestimating, the one or more processors are configured to: warpcoordinates of the depth image of the previous frame into coordinates ofthe depth image of the current frame based on position information orpose information of a camera, and estimate an area having an inestimabledepth value in the depth image of the current frame using the warpeddepth image of the previous frame.
 12. The apparatus of claim 10,wherein, for the determining of the occlusion accumulation image of thecurrent frame, the one or more processors are configured to: initializea pixel with a depth difference accumulation value being less than orequal to a first threshold value in the occlusion accumulation image.13. The apparatus of claim 10, wherein, for the determining of theocclusion accumulation image of the current frame, the one or moreprocessors are configured to: initialize a pixel with a depth differencevalue being less than or equal to a second threshold value in theocclusion accumulation image.
 14. The apparatus of claim 10, wherein,for the outputting, the one or more processors are configured to: obtainan area including one or more pixels having a depth differenceaccumulation value being greater than a first threshold value in theocclusion accumulation image, and output a masking image representing anarea of the moving object based on the obtained area.
 15. The apparatusof claim 10, further comprising a memory storing instructions that, whenexecuted by the one or more processors, configure the one or moreprocessors to perform the estimating of the depth image of the currentframe, the determining of the occlusion image of the current frame, thedetermining of the occlusion accumulation image of the current frame,and the outputting of the area of the moving object.
 16. Aprocessor-implemented method of detecting a moving object, the methodcomprising: acquiring a current depth image including an area in which adepth value is not obtained by a depth sensor; estimating the currentdepth image, including the area not obtained by the depth sensor, bywarping a previous depth image into coordinates of the current depthimage; and determining a current occlusion image by calculating adifference between the estimated depth image and the previous depthimage; determining a current occlusion accumulation image by adding thecurrent occlusion image to a previous occlusion accumulation image; andoutputting an area of a moving object based on the current occlusionaccumulation image, wherein the determining of the occlusionaccumulation image of the current frame comprises estimating a depthdifference accumulation value of a newly discovered area in theocclusion accumulation image of the current frame based on a similaritybetween a depth value of the depth image of the current frame and theocclusion accumulation image of the previous frame.